Inking units for regulating the quantity of ink dispensed on a duct roller from the ink duct of a printing press are known to include zone dispensing elements which are adjustable relative to the duct roller and which have a dispensing edge cooperating with the duct roller to define a dispensing gap with the edge movable relative to the duct roller substantially radially and with the dispensing edge being disposed on a blade releasably retained on an adjuster. German patent No. 3 0303 774 discloses an inking unit of this kind.
Such inking units are used in printing presses, more particularly offset presses, to ensure accurate and reproducible adjustment of ink quantity. Therefore, it is necessary to adjust the quantity of ink to different extents widthwise of the press and in zonally independent manner. The difficult part of this problem is the need for extremely accurate alignment of the various dispensing elements for very reduced ink layer thicknesses. The necessary outlay and the risk of the dispensing edge of the various dispensing elements being damaged should not be underestimated. If discrete dispensing elements or the blades on their adjusters are aligned inaccurately, what are known as "edge carriers" may arise which make it impossible to find an accurate zero setting for the particular dispensing elements concerned. Since in such cases the printer endeavors to engage the dispensing element completely with the duct roller by further adjustment in the particular zone concerned, damage easily arises because of increased wear. Nevertheless, it is an important objective to ensure accurate adjustment.
According to the above-mentioned German patent No. 3 030 774, the dispensing edge is disposed on a push-shoe having spring steel plates or the like, on discrete ink-dispensing elements in the form of adjusters. The plates, with their hard resilient substance, form the dispensing edge and are secured in a resilient embedding composition. Also, the composition is formed with a recess behind the dispensing edge. This dispensing element reduces the wear to some extent because of the increased strength of the dispensing edge and because of the resilience thereof. Ease of service is improved by simple replacement of the shoe which can also latch in the ink-dispensing element by way of cast-on protuberances.
The alignment of the shoe relatively to the adjuster is not variable in the ink dispensing element just described--i.e., the dispensing edge cannot be adjusted independently relative to the adjuster. Errors of manufacture are therefore fully transferred to the assembled unit and affect the accuracy of ink dispensing. In all, the ink-dispensing element suffers less from wear but does not ensure that the adjustment of the thicknesses of thin ink films is always accurate. Consequently, accurate alignment and equalization of the dispensing edge of the various dispensing elements relative to one another causes problems just as severe as adjustments relative to the duct roller.
For example, if a slightly inclined ink-dispensing element was to be operated at zero ink film thickness, the dispensing edge would have to bend in order to interrupt the supply of ink completely. This bending is possible but sets a wrong zero for the opening of the dispensing gap, for when the ink-dispensing element returns, such gap is initially opened only on one side, with the result of underinking. Also, the power consumption relative to the duct roller is such that it bends by something like 10 times the permissible gap for minimum inking between the dispensing edge and the roll surface. Consequently, independent widthwise adjustment of the dispensing elements cannot be ensured.